Method of making uniform corrosion anodes



Patented Dec. 26, 1933 METHOD OF MAKING UNIFORM CORROSION ANODES George Fellmeth Geiger, New York, N. Y., as-

signor to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Original application March 12,

1930, Serial No. 435,356. Divided and this application September 28, 1931.

5 Claims.

This invention relates to a method of making improved anodes employed in the electrodeposition of metals, particularly nickel anodes for the electrodeposition of nickel.

In particular the invention pertains to a novel method of making nickel anode of the cast or rolled type by yhich more uniform corrodibility with 'a smooth surface and an increased solubility are obtained than has heretofore been possible. Such advantages, obtained in a practical and commercial manner, have long been sought.

The main objects of this invention are, therefore, to produce, by a novel method, an improved nickel anode by which more uniform and satisfactory plating is accomplished.

It is to be understood that the improved anode herein described may be either cast or rolled, and have therein a percentage of oxygen, and/or sulphur which are the preferred elements or have an element or materials acting similar thereto for the purpose set forth. Such other elements or materials may be manganese and/or silicon.

n the use of these improved anodes several advantages, not heretofore known, have developed. These advantages are: the producing of much smoother plating work; that there is uniform corrosion in a larger majority of baths, which condition has not been possible with other anodes available today; that the anodes are more readily soluble; that it is possible to new main-' tain uniform conditions in the electro-plating bath by reason of the fact that the anodes do not dissolve too easily or not too difficultly; that the improved anodes corrode in a manner with a smooth surface thereby substantially eliminating droppings and the presence of slimes.

The invention should not be limited to the production of anodes alone, as the improved alloy has other advantageous uses, such as the production of special cast or rolledproducts.

Acknowledgment is made of the improvements in carbon-free nickel by Merica and Kayes, U. S. Patent No. 1,811,696. granted June 23, 1931, and improvements in Rolled carbon-free anodes by Mudge, Serial No. 221,146. The present improvement gives beneficial results over the disclosures inthose applications.

In plating work. especially in nickel-plating, one of the main desires has been to obtain smooth and satisfactory plating. The attainment of this Serial No.

object has been very difl'icult in the past, and the anodes which have shown the best results heretofore have been known as oxygen-bearing or depolarized anodes. The most preferred form of that type was a rolled anode. The cast oxygen-bearing anodes were not as satisfactory as the rolled anode of that type.

Again, in the plating work, without good control of plating solutions and unless a very satisfactory anode is employed, rough plating results. It appears that the greatest trouble of platers today is in obtaining sound and smooth plating. Rough plating is produced when bad anodes are employed, and usually results from small particles of nickel. or impurities, being carried from the anode to the wo k and attaching themselves thereto as solid bodies, and thereafter building themselves up in size. This building up is natural as the tops or summits of these particles are nearer to the anodes and the current will normally pass to these high spots and not readily to the valleys between the particles. It will therefore be seen that the resulting plating presents a series of hills and dales or valleys in its surface.

It is usual after the plating to brighten same by bufling. It has been found during the bufling process that these particles or hills are pulled out leaving holes in the plating thereby exposing the base metal. The exposure of this metal permits of rusting or corroding to start immediately. With such bad plating results, the nickel plating does not serve its intended purpose, i. e., protecting the metal.

It will therefore be seen that it is highly desirable to obtain and use improvedanodes which have uniform corrosion and which practically eliminate particles of nickel in the bath and which permit the production of smooth and satisfactory plating in a quick and eificient manner.

The improved anodes herein to be described have been found by experience to give the desired uniform corrosion; to have less sludge on themselves or in suspension or in the bottom of the bath; to substantially eliminate the finding of nickel particles in the bottom of the bath; to give material increase in solubility; and to corrode with a smooth surface.

Considering these advantages more in general in order to appreciate the reasons therefor, it is found that the advantage of uniform corrosion resides in the fact that substantially all of the nickel in the anode is used for its intended purpose-i. e., plating.

With the improved anode herein very much less sludge is produced, in fact, substantially none. When the term sludge is employed it usually refers to some sort of insoluble material. Whatever very small amount may manifest itself, it is not detrimental. It may be found on the anode, or suspended in solution; or in the bottom of the bath.

By the statement that there are substantially no nickel particles in the bottom of the bath, it is meant that the improved anode corrodes with such uniformity that the rate of eating or corrosion of the grains themselves is substantially the same as the rate of eating of the material in the grain boundaries. When particles of nickel are found in the bath, it means that the material between the grains, or within the grain boundaries, as it is often called, is eaten away at a much faster rate than the grains themselves and the grains fall from the anode before being eaten or dissolved. The falling of such grains means that they either drop to the bottom of the bath and are completely lost for plating purposes, or are held in suspension and carried to the surface of the member being plated with the attendant unsatisfactory hill and dale plating results above indicated. It may also be noted at this point that the eating and corroding within the grain boundaries may be and often is sufiicientlwfast to eat around several grains heldtogether. In such an event a whole lump of nickel falls from the anode to the bottom of the bath and is lost for plating purposes.

In the improved anode it has been found by microscopic examination of a partially corroded anode that there is substantially no faster eating of the material in the grain boundary than in the grains themselves. I

The improved anode permits of very materially increased'solubility which means less demand of electrical power to transfer the nickel from the anode into solution, and when it is understood that a large number of these anodes are employed, the saving in the total electrical energy is very material and important.

The feature of corroding with a smooth surface is also important. When it is possible to obtain an anode that cprrodes with a smooth surface, it is found that a lacy structure, found so often in other anodes, is eliminated. It has been found by investigation that a lacy structure or net work holds sludge and impurities on or at the surface of the anode and acts as an insulator to the action of corrosion, thereby preventing a ready transfer of the nickel into the bath. In any event the efliciency of plating is very materially reduced when the lacy structure is present. The use of the word corrosion herein is usually employed to denote the action of transferring the nickel into the solution.

From another viewpoint, the impurities permit the starting up of local actions, which create depressions and the formation of the net work. This net work is particularly disadvantageous as it holds sludge and thereby prevents the nickel from being readily transferred into the bath. As the corrosion proceeds, portions of the net work separate from the anode in particle or lump formation. While the foregoing may be a satisfactory theory of what happens, it is to be understood that it is only the most likely definition. In any event, practice and the investigations show that when some sort of lace or net work is present, rough plating results.

It has been found with the use of the improved anode herein that most of the caution required in maintaining the bath at a definite workable condition or neutrality, is substantially eliminated. With this advantage a less skilled attendant may be employed in the plating work. It is believed that the reason for this advantage is that substantially all of the electrical energy employed is consumed for its desired purpose, 1. e., transferring the nickel into the solution or bath.

It has been found that the improved nickel anode which has given the satisfactory results and advantages as above outlined, may be readily produced, in substantially any physical form of anode heretofore known, by adding thereto a material or materials which may readily be dispersed throughout the grains of the nickel and throughout the intergranular material. Such ad vantageously added materials are found to be preferably oxygen, with sulphur or similar material in regulated amounts, the sulphur content preferably ranging between .002 and .020 per cent. In some types of anodes just sulphur, or its equivalent in desired amounts is added to give the improved results. It has been found preferable, however, to employ a lower amount of sulphur in order to reduce the brittleness of the product. For a preferred commercial form and commercial production it is desirable to have the sulphur within a range of .002 and .005 per cent, although a range of 0.0035 to 0.0075 per cent of sulphur gives eminently desirable results in practice.

It is believed that the added material or materials are dispersed substantially uniformly throughout the grains and throughout the material in the grain boundaries. This may or may not be the actual fact, but in any event the addition of the materials described above produces very beneficial and improved results. amination of the products microscopically shows what is believed to be uniform distribution.

While the presence of some sulphur has been heretofore known, it has always been indicated that it is undesirable from the standpoint of hot working and should be eliminated. It has now been found, especially for anodes and other products, that the presence of sulphur, in controlled amounts, will still permit good hot forging and rolling, and will give, in addition, in plating work, great improvement in the plating, and in the efliciency of operation.

Thus, by controllingthe addition of the sulphur in various types of anodes, it has been found that a very material increase in efliciency, in the uniformity of corrosion, and smooth satisfactory plating have been obtained without completely sacrificing hot rolling properties.

It has also been found that by controlling the amount of sulphur within preferred limits, and this in anodes of the oxidized, cast or rolled type, the advantages above outlined are noted to a very marked degree. In any event these oxidized, cast or rolled anodes which have sulphur added to them in controlled amounts, are materially better than such anodes without the sulphur.

The nickel oxidized anodes which have nickel oxide added to them within .02 to .25 per cent, have been found to give very beneficial results with sulphur present between .002 and .020 per cent. The preferred percentages in an anode which has very satisfactorily shown the improved The exresults, were orygen .10.20 per cent, and sulphur 15 outlined. Thus.

While the preferred disclosure illustrates the.

advantages of the addition of oxygen and sulphur within satisfactory ranges, it is'to be understood that other materials may be employed for obtaining substantially the same results in producing a satisfactory anode which will give uniform corrosion and most of the other advantages above it will be seen that certain elements or compounds may be substituted for the sulphur. Desirable elements or compounds or equivalents for the sulphur have been found to be manganese and silicon, the former being employed in about .10-.24 per cent, and the latter in about .10-.30 per cent. It was also found that the oxygen content when adding these elements, could be varied from .02 to .25 per cent. A satisfactory balance between the quantities of sulphur or its equivalents on the one hand, and the oxygen on the other, may be made.

In producing the improved anodes herein, it is usual to proceed as follows: The nickel employed is first melted down, then a desirable amount of sulphur or its equivalent is added in order to obtain substantially uniform distribution thereof throughout the mass, the bath is then flapped, or treated as by adding nickel-oxide or in any desirable manner to give the desired oxygen content. The melt is then tapped and poured into ingot form, and afterwards forged and rolled to an anode or other form. The anodes may or may not thereafter be submerged in an alcohol-water bath to reduce any oxide coating which may be present on the metal.

In the manufacture of substantially all types of anodes, including heat treated anodes, there has been found to be formed thereon a relatively thin coating or skin which has been termed passive nickel. In most instances it is desirable to remove this coating or skin so that the corrosion may start immediately upon the introduction of the anode into the bath.

It has been found with oxygen-bearing and other anodes which have the sulphur content or its equivalent included therein, that once the coating or skin has been removed, there is no further formation of such skin, even though the anode may be withdrawn from the bath several times. This is an important advantage not heretofore known or disclosed.

It may be noted that the presence of the skin is very detrimental at the start of the operation of plating as actual corrosion is very materially hindered and the skin drops into the tank and forms part of the sludge. In the event pieces of skin are of such length and a free end thereof should extend to and be brought into contact with the article being plated, there will be a shortcircuiting of the anode and the cathode or piece being operated upon.

In the former practice it is found that when the anodes are removed to be washed, or the bath is changed or modified, that a new skin forms on the old type of anodes. It is of particular advantage that there shall not be a formation of skin every time an anode is dried or handled. The improved anode herein does not have this disadvantage. Thus greater efficiency in the plating work is accomplished with the improved anodes herein described.

It has been found that the coating or skin may by experience with anodes be readily removed by subjecting them to corrosion in a 3-5 per cent solution of hydrochloric acid. This is known as a deskinning operation. The anode may be made more suitable for deskinning by quenching after hot rolling from a temperature 1700-1800 degrees Fahrenheit in an alcohol water solution containing one part alcohol to eighty parts of water. The

alcohol bath has been found satisfactory for the purposes, but other baths may be employed, if desired.

When the plating bath is readily maintained at its preferred slight acidity of pH.=5.4 to 6.7 the improved anode herein permits the continuance thereof for a much longer period than with the old types of anodes. In the event of slight changes in the composition of the bath, then the anodes of controlled oxygen and sulphur content, such as are disclosed herein, will permit the continuance of good uniform corrosion under these poorer and less desirable bath conditions.

It will be seen from the foregoing that with a controlled amount of oxygen and/or sulphur, or its equivalent in the anode, an improved anode will be produced. This effective anode has eliminated many prior plating troubles, insured smoother and better plating and easier control of the bath. There is consequently greater efficiency of operation, a more uniform corrosion and increased solubility. Less sludge is formed and there are practically no nickel particles in the bottom of the bath.

From microscopic examinations of the improved anodes, it appears that the oxygen'and/or sulphur, or the materials which act as the latters equivalent, or the reaction products thereof, are substantially uniformly distributed throughout the grains and throughout the material in the grain boundaries.

It will also be seen that the improved article of manufacture comprises an anode whiiih gives improved electro-deposition through improved corrosion, and is of a type that results in substantially no metallic anode droppings, that gives a smooth anode surface and substantially no anode sludges, all of which are recognized as characteristics of the most efficient functioning anodes.

It is to be understood that various changes and modifications may be made, but that such changes and modifications are to be considered as bein within the scope of the invention as outlined in the following claims.

This is a divisional application of my application Serial No. 435,356, filed Mar. 12, 1930.

What. is claimed-is:

1. In the production of nickel articles the steps of melting down thenickel-bearing material, adding sulphur to the melt in a positive manner, controlling said positively added sulphur to an amount within a range of 0.002 per cent to 0.020 per cent, and pouring.

2. In the production of nickel anodes the steps of melting commercial nickel, positively adding .002-.020 per cent sulphur to the melt, adding .02-.25 per cent oxygen by flapping, controlling the sulphur. and oxygen contents within the said ranges, pouring the melt, forging and rolling the ingot formed to anode shapes, and submerging the anodes in an alcohol-water bath from a temperature of 1700-1800 degrees Fahrenheit, and deskinning said anodes by'subjecting them to the action of a dilutesolution of hydrochloric acid.

3. In the production of nickel anodes, the steps itively adding subs, sulphur to the melt, and .10-.20 per and rolling the ingot of melting commercial nickel, positively adding .002-.020 per cent sulphur to the melt, adding .02.25 per cent oxygen by flapping, pouring the melt, forging and rolling the ingot formed to anode shapes, and submerging the anodes in an alcohol-water bath from a temperature of 1700- 1800 degrees Fahrenheit.

GEORGE FELLMETH FWZTGER. 

